RV Repair: drive line shudder, piece driveshaft, driveline shop

Question
have a 99 chevy p30 chassie have a drive line shudder had all tires replaced u joints looked at still shudders !!!!! do you know what it is ? do you think it is u joints or drive shaft ?

Answer
You are actually asking a Chevrolet question but I will take a stab at it.
Shutter is usually the sign of bad u-joints especially if you hear a "clunk" when putting it in gear.  It could be an unbalanced driveshaft (or bent) or could be something in the transmission. If you have a two piece driveshaft, it could be the carrier bearing in the bracket between the two.
Take it to a driveline shop, have them crawl under it and rule in or out the above possibilities.